The invention relates to a display unit, in particular for a motor vehicle, having a light source radiating into an optical conductor, in particular for backlighting of a transparent dial.
Display units of the above type are used, for example, as tachometers or pedometers in present-day motor vehicles and are generally known. The dial of such a display unit has markings in the form of numbers, symbols or scale marks which stand out from the remaining regions by their transparency or their coloring. This dial consists, for example, of a colored, preponderantly transparent film which is applied to the optical conductor. A lamp is arranged as light source behind the optical conductor. The lamp is used to launch into the optical conductor light which reaches a viewer through the dial.
It is disadvantageous in such a display unit that the dial regions adjacent to the light source are more strongly transilluminated than regions more remote from it. The dial is therefore transilluminated non-uniformly, with the result that, for example, the light source can be detected through the dial at a bright spot by the viewer and thus hinders readability. In practice, this disadvantageous is at least partially offset by a multiplicity of light sources arranged as uniformly as possible. In this case, the high outlay associated therewith, and the substantial space requirement are disadvantageous.
Furthermore, it is seen as disadvantageous in the case of such display units that even the smallest amount of damage, irregularities or soiling of the optical conductor become visible on the dial to the viewer. Soiling necessitates troublesome cleaning of the display unit. Furthermore, means for fixing the optical conductor on the dial can lead to formation of shadows which likewise have to be evened out.
The invention is based on the problem of configuring a display unit of the type mentioned at the beginning such that the dial can be lit with the smallest possible outlay without differences in brightness visible to a viewer.
This problem is solved according to the invention by virtue of the fact that the optical conductor is arranged essentially in a plane inclined with respect to the dial, the light source shining into a section of the optical conductor inclined away from the dial. As a result, a portion of the light led into the optical conductor is coupled out at its boundary surface, and the remaining portion of the light is guided inside the optical conductor further in the direction of the dial. In this case, a relatively large portion of the light emerges at the section of the optical conductor which is inclined toward the light source and is spaced relatively far from the dial, while a decreasing portion of the light emerges at a reduced spacing from the dial. The impression of brightness is thereby evened out for the viewer over the entire surface of the dial. In particular, in this case a light source shining into a section of the optical conductor suffices to enable a comparatively simple design to be achieved, which at the same time can be produced with a low outlay. Put simply, the optical conductor can be considered, on the one hand, as an optical conductor and, on the other hand, like an obliquely positioned mirror as reflector. Furthermore, damage or dirt particles on the outside of the optical conductor remain largely invisible to a viewer. Again, the uniform and bright emission of light also renders it possible to realize dials with a so-called positive representation, in the case of which dark, opaque numerals are arranged on the transparent, bright dial, so that the lighting of a pointer can be eliminated.
In this case, a particularly advantageous embodiment of the invention results from the fact that the optical conductor has a cross-sectional surface decreasing from a section of the optical conductor inclined toward the light source to a section of the optical conductor inclined toward the dial. Due to this essentially wedge-shaped form of the optical conductor, the light led into it strikes the boundary surface of the optical conductor at an increasingly steeper angle, as a result of which the reflection is reduced and an increasing portion of the light emerges from the optical conductor. It is thereby possible to achieve a quantity of light emerging uniformly over the entire length of the optical conductor, and thus optimum lighting of the dial.
A particularly useful development of the invention is also achieved when the optical conductor has a light outcoupling surface designed as a structured surface. It is possible by means of such a configuration of the outer surface to achieve pinpointed outcoupling of the light in a desired region. It is thereby also possible for specific subregions of the surface to be lit to be optically emphasized. The structured surface can be arranged in this case both on an outer surface of the optical conductor inclined toward the dial, and on an outer surface of the optical conductor inclined away from the dial. The structured surface can consist for this purpose of depressions, for example notches of different dimensions, a rough surface, a printed surface or a mat surface. In particular, the light outcoupling surface can also comprise a combination of differently structured surfaces, in order thus to achieve a different emergence of light in different sections of the optical conductor.
A development of the invention which is likewise particularly expedient is achieved by virtue of the fact that the optical conductor has at least one boundary surface which runs in its cross section and has an altered transmission. This boundary surface causes an intensified emergence of the incident light, thus achieving a brightness of a respective subregion which can be reliably determined in advance. Such boundary surfaces can be arranged for this purpose at a different spacing from one another which, in particular, can be made to be smaller in the region inclined toward the surface to be lit, with the result that a correspondingly increasing portion of the light led in is coupled out.
The optical conductor could have a cutout for guiding through a pointer shaft. A particularly favorable embodiment of the invention is, by contrast, also achieved by virtue of the fact that the optical conductor runs approximately helically from a plane set back from the dial to the plane of the dial. It is possible as a result to light a dial, for example an annular one, without differences in brightness, the pointer shaft being arranged in the central region, and the guidance of the light not being hindered thereby.
It is also particularly advantageous when the optical conductor bears against the dial with its section averted from the light source. As a result, the light can be led directly into the dial so that, on the one hand, it is possible to achieve a further increase in the brightness of the dial lit in such a way. On the other hand, the light for lighting further displays can be relayed to the display unit.
One embodiment of the invention is particularly useful by virtue of the fact that the light source is arranged on a printed circuit board together with the section of the optical conductor inclined toward the light source. As a result, the mounting operation can be substantially simplified, and thus a space-saving configuration can be achieved at the same time. For this purpose, the light source makes contact with the printed circuit board and shines directly into the optical conductor.
It is particularly favorable in this case when the section of the printed circuit board spanned by the optical conductor is provided for the arrangement of further electric components. As a result, the space available below the optical conductor can be optimally used, and thus the overall size of the display unit can be reduced.
An advantageous development of the invention is also achieved by virtue of the fact that the optical conductor has a middle section inclined toward the dial and two end sections inclined away from the dial into which one light source shines in each case. As a result, it is possible simultaneously to achieve a stable configuration of the optical conductor which is easy to mount, and to increase the lighting intensity which can be achieved by means of the optical conductor. It is also possible in this case to use light sources with a different color in order, for example, to emphasize a subregion of the dial optically, or to represent the achievement of a critical value of the display unit in a signal color.
It is also particularly expedient in this case when the optical conductor is provided with a reflecting element on an outer surface averted from the dial. This reflecting element prevents the undesired emergence of light at an outer surface averted from the dial, in particular the underside of the optical conductor, and thereby reduces the losses. For this purpose, the reflecting element can be designed, for example, only as a reflecting coating applied to the underside of the optical conductor, or as a reflector which is connected to the dial and encloses the optical conductor.
A particularly advantageous development of the invention is achieved in this case by virtue of the fact that the light source is a light-emitting diode (LED). A form of the display unit which simultaneously saves energy and can be produced without any problem is thereby realized. The light-emitting diode can be designed for this purpose preferably as a component (SMD) which can be surface-mounted, with the result that the mounting process can be further simplified.
Detouring the light, and thus reducing the light yield, when launching it into the optical conductor can be avoided when the direction of emission of the light source is not vertical, but approximately parallel to the printed circuit board. It is particularly favorable when the light source is designed for emitting the light in a fashion directed obliquely upward. As a result, light emanating from the light-emitting diode can shine in directly in the direction of the optical conductor arranged obliquely between the plane of the dial and the printed circuit board running parallel thereto. Further optical components for deflecting the light are therefore not required, with the result that no losses occur, or only slight ones. For this purpose, the light-emitting diode can, for example, also bear directly against the optical conductor and thus permit light launching which is further improved.
Another particularly useful embodiment of the invention is also achieved by virtue of the fact that in addition to the first light source the display unit has at least one further light source of different color. It is possible as a result to represent the change in the color of the surface lit by means of the optical conductor. For example, this change in color can be performed when a specific pointer position of the display unit is reached, and the associated value can thereby be emphasized optically. In the same way, the change in color can also be performed by means of a multicolored light-emitting diode which emits light with a different color spectrum depending on how it is driven.
Also particularly useful is a development of the invention in which the dial and a liquid crystal display (LCD) arranged approximately in the plane of the dial can be lit simultaneously by means of the optical conductor. As a result, it is possible to eliminate a separate light source for the liquid crystal display. At the same time, the free space below the optical conductor can be used for a controller, in particular a driver of the liquid crystal display.